The present invention relates generally to attaching electrical components to printed circuit boards, and more particularly, to adapters for surface mount devices.
An integrated circuit combines numerous active and passive electrical circuitry elements on a single device called a die or chip. These integrated circuits are interconnected by attaching them to printed circuit boards. Such circuits are inherently small and fragile devices. Thus, they are usually embedded in a substrate called a chip carrier or package before they are attached to the printed circuit board. Protruding from the package are a number of electrical conducting leads. The conducting leads may protrude from the package by extending through the bottom of the package (e.g., pin or pad grid arrays), may be arrayed along two edges of the package (e.g., dual in-line pins), or may fan out from the edges of the package (e.g., gull wing and jay pins).
The wiring on printed circuit boards may include thin metallic strips embedded in an insulating material. These strips interconnect leads from different circuit packages mounted on the same board. For all of the required connections, the boards may have several layers of interconnected wiring. The wiring is used to determine the placement of the integrated circuit packages on the board. Also, the wiring is employed to route electrical signals among the integrated circuits. The leads may connect to the wiring in a variety of ways. One technique includes drilling holes in the board and through the wiring at appropriate locations, inserting the leads through the holes, and making mechanical and electrical attachments among the leads, the wiring, and the holes. Another technique is called surface mount technology (SMT). This method includes arranging contact pads on the surface of the printed circuit board. The pads are used to deliver electrical signals to the leads and to the appropriate embedded wires. Leads may be placed on top of the pads and mechanically and electrically attached.
SMT is widely used for high speed digital communications. Typical packages include plastic leaded chip carriers (PLCC), dual in-line packages (DIP), single in-line packages (SIP), small outline packages (SO), and small outline T-leaded packages (SOT). To test or prototype these type devices, custom device-specific evaluation boards supplied by the manufacturer are required. This is because each device has a different specific footprint. In many cases, a large number of the device-specific evaluation boards are required. As a result, prototyping can be limited. For example, if a certain device-specific evaluation board was not available, an entire prototype procedure may be impeded.
Also, these high speed devices require controlled impedance inputs and outputs that are not easily implemented in a general printed circuit board configuration. Certain commercially available surface-mount to DIP and SIP adapters have been employed. However, these adapters are not suitable for high frequency applications. These adapters have long traces between the device footprint and the pins of the DIP or SIP. This can create excessive noise in the resulting signal, and also, poor performance from the integrated circuit. Additionally, critical components, such as a power supply pin, must be located on the printed circuit board. As a result, long wire traces must be used to interconnect the device to other components in the system. This can also contribute to faulty signal and circuit operation.